Method and device for automatically determining the contours of heights of the relief of a geographical area

Abstract

A device for automatically determining the contours of heights of a relief includes an image receiving unit configured to receive an image of a predetermined geographical area. The image includes altimetric data. A background surface elimination unit eliminates the background surface of the relief. The background surface illustrates gradual variations in one or more altitudes of the geographical area. A top-hat algorithm having an adjustable structuring element can be used. A thresholding unit generates a binary image which only contains those reliefs having heights above a threshold value. An extracting unit extracts rough contours of heights of the relief from the binary image. A simplifying unit obtains a set of polygons by simplifying the rough contours. The polygons illustrate contours of the heights of the relief of the geographical area.

The invention claimed is: 
     
       1. A method for automatically determining contours of heights of a relief, of a geographical area (ZO), the method comprising:
 a) on the basis of an image of said geographical area (ZO), which contains altimetric data of points therein, a background surface of the relief which illustrates gradual variations in altitudes of said geographical area (ZO) is eliminated, by implementing a top hat algorithm, which uses a structuring element ( 28 ) which is adjustable; 
 b) on the basis of step a), thresholding is performed on the image of said geographical area (ZO) to form a binary image (IB) of the relief seen from above, containing only reliefs having heights above a threshold value which is adjustable, wherein the threshold value is calculated using a noise tolerance parameter wherein T=k−σ, wherein k is a coefficient of standard deviation and a is the standard deviation of altitudes in the altimetric data; 
 c) from this binary image (IB) which comprises two different types (Z 1 , Z 2 ) of area, rough contours of the heights of the relief are extracted, illustrating the boundaries between these two different types (Z 1 , Z 2 ) of area; and 
 d) said rough contours are simplified so as to obtain a set of polygons (P 1 , P 2 , P 3 ) illustrating the contours (C 1 , C 2 , C 3 ) of the heights of the relief of said geographical area (Z 0 ). 
 
     
     
       2. The method according to  claim 1 , wherein in step d) said set of polygons (Pi, P 2 , P 3 ) is superimposed consistently on an image (F) of said geographical area (ZO) so as to obtain a composite image (IF). 
     
     
       3. The method according to  claim 1 , wherein in step sphere is used as a structuring element. 
     
     
       4. The method according to  claim 1 , wherein in step b) the thresholding is performed so as to preserve only one or more reliefs which are high enough to be exploited. 
     
     
       5. The method according to  claim 1 , wherein in step d) simplification algorithm is implemented which uses a tolerance parameter indicating a degree of simplification, which is adjustable. 
     
     
       6. The method according to  claim 1 , wherein, in an additional step, said set of polygons (P 1 , P 2 , P 3 ) is analysed in order to define at least one attribute making it possible to characterise said polygons (P 1 , P 2 , P 3 ). 
     
     
       7. The method according to  claim 1 , wherein said attribute is highlighted in a composite image (IF). 
     
     
       8. The method according to  claim 1 , wherein at least some of the following attributes, which are independent of one or more altitudes of the relief, are determined:
 a distance from a target; 
 at least an area of a polygon; 
 at least a simple majorant rectangle which is associated with a polygon; and 
 at least a majorant convex polygon. 
 
     
     
       9. The method according to  claim 1 , wherein at least some of the following attributes, which are dependent on one or more altitudes of the relief, are determined:
 a mean altitude; 
 a standard deviation of the altitudes; 
 a maximum altitude; and 
 high points. 
 
     
     
       10. The method according to  claim 9 , wherein, to determine said high points, points having local maximum heights (M 1 , and M 2 ) are sought, by means of a threshold which is adjustable, and all the points found which are outside said rough contours are excluded.